This invention relates to meter electronics for a Coriolis flowmeter. More particularly, this invention relates to meter electronics that has a signal conditioner that is remote from a host system and is capable of being intrinsically safe. Still more particularly, this invention relates to meter electronics that have a signal conditioner that allows conventional 2 or 4 wire cable to be used to supply power to a Coriolis flowmeter.
It is known to use Coriolis effect mass flowmeters to measure mass flow and other information with respect to materials flowing through a pipeline as disclosed in U.S. Pat. No. 4,491,025 issued to J. E. Smith, et al. of Jan. 1, 1985 and U.S. Pat. No. Re. 31,450 to J. E. Smith of Feb. 11, 1982. These flowmeters have one or more flow tubes of a curved or a straight configuration. Each flow tube configuration in a Coriolis mass flowmeter has a set of natural vibration modes, which may be of a simple bending, torsional, radial, or coupled type. Each flow tube is driven to oscillate at resonance in one of these natural modes. The natural vibration modes of the vibrating, material filled systems are defined in part by the combined mass of the flow tubes and the material within the flow tubes. Material flows into the flowmeter from a connected pipeline on the inlet side of the flowmeter. The material is then directed through the flow tube or flow tubes and exits the flowmeter to a pipeline connected on the outlet side.
A driver applies a vibrational force to the flow tube. The force causes the flow tube to oscillate. When there is no material flowing through the flowmeter, all points along a flow tube oscillate with a substantially identical phase. As a material begins to flow through the flow tube, Coriolis accelerations cause each point along the flow tube to have a different phase with respect to other points along the flow tube. The phase on the inlet side of the flow tube lags the driver, while the phase on the outlet side leads the driver. Sensors at two different points on the flow tube produce sinusoidal signals representative of the motion of the flow tube at the two points. A phase difference of the two signals received from the sensors is calculated in units of time. The phase difference between the two sensor signals is proportional to the mass flow rate of the material flowing through the flow tube or flow tubes.
It is a problem that a 9-wire cable must be used to connect meter electronics to a flowmeter assembly. For purposes of the present discussion, meter electronics include all of the circuitry needed to produce drive signals and to process signals from the sensors and a flowmeter assembly includes at least one flow tube, an affixed driver, and sensors needed to measure the oscillation of the flow tube. The 9-wire cable for connecting the meter electronics to the flowmeter assembly includes two wires that connect the meter electronics to the driver, two wires that connect the meter electronics to a first pick-off, two wires that connect the meter electronics to a second pick-off, and three wires for connecting the meter electronics to a temperature sensor.
The 9-wire cable is a custom cable and is expensive to produce and is therefore expensive for a user of a Coriolis flowmeter to purchase. The expense of 9-wire cable is a particular problem when the user of a Coriolis flowmeter wishes to move the meter electronics to a control area remote from the flowmeter assembly. The 9-wire cable must be installed the entire length between the meter electronics and the flowmeter assembly. The cost of such 9-wire cable increases greatly as the distance between the meter electronics and the flowmeter assembly increases. It would be a particular advantage if conventional 2-wire or 4-wire cable that is relatively inexpensive and readily available to users could be used to connect the flowmeter assembly to the meter electronics.
A further problem in designing meter electronics is that the meter electronics may be used in an explosive environment containing a volatile material. For purposes of the present discussion, an explosive environment is a system that includes a volatile material which can be ignited if a spark, excessive heat, or excessive energy is introduced into the environment. One manner in which a meter electronics may operate in an explosion environment is to be enclosed in an explosion proof housing. An explosion proof housing is a housing that is designed to ensure that a spark or excessive heat from inside the housing does not ignite the volatile material in the environment outside the housing.
In order to make a device explosion proof, methods including encapsulation, pressurization, and flameproof containment may be used. Each of the above methods encloses a device to prevent the volatile material from contacting the device where heated surfaces of the device or sparks from circuitry in the device may cause an ignition of the material. If a material ignites inside an enclosure, any gaps or openings in the enclosure must provide a flame path of a sufficient length to cool the material as the material escapes from the enclosure. The cooling of the hot material prevents the hot material from igniting the volatile material outside the enclosure.
A second solution is to make the meter electronics intrinsically safe. An intrinsically safe device is a device in which all the circuitry in the device operates under a certain low energy level. By operating under a certain energy level, the device is ensured not to generate a spark or sufficient heat to cause an explosion even if the device fails in some manner. The power level needed to make a device intrinsically safe are determined by regulatory agencies such as UL in the United States, CENELEC in Europe, CSA in Canada, and TIIS in Japan.
The above and other problems are solved and an advance in the art is made by a signal conditioner in accordance with this invention. A first advantage of this invention is the 9-wire cable to a Coriolis flowmeter assembly may be eliminated even in flowmeters where a power supply may be remote from a Coriolis flowmeter assembly. A second advantage of this signal conditioner is that the entire meter electronics do not have to be enclosed in an explosion proof housing. Instead, a signal conditioner may be used that operates at a power level below the required energy and/or power threshold needed to be intrinsically safe. Therefore, the signal conditioner does not have to be enclosed in an explosion proof housing if the leads to and from the signal conditioner do not carry energy and/or power at a level above the threshold for being intrinsically safe.
The meter electronics of this invention eliminate the need for conventional 9-wire cable to connect a flowmeter assembly to the meter electronics in a Coriolis flowmeter. Instead, a conventional 2-wire or 4-wire cable can be used to supply energy and/or power to a signal conditioner from a host system. The signal conditioner can generate the drive signal, can receive sensors signals from motion and temperature sensors affixed to a flow tube, and can process the signals from the sensors to generate information about the properties of the material flowing through the flow tube.
The signal conditioner is connected to the driver and sensors by 9 separate leads that are distinct from the conventional 9-wire cable typically used to connect the meter electronics to the 9 separate leads. After processing the signals, the signal conditioner may transmit information relating to properties of the material over 2 separate wires in a conventional 4-wire cable or over the 2-wires supplying power in a conventional 2-wire cable.
In order to make the signal conditioner capable of being intrinsically safe, the signal conditioner includes host-side protection circuitry and flowmeter assembly protection circuitry. The host side protection circuitry prevents energy and/or power in excess of an intrinsically safe threshold from being applied by the signal conditioner to the leads connecting the signal conditioner to the host system. The intrinsically safe threshold is the level of energy and/or power dictated by various agencies to ensure that a spark or heat from the circuitry does not ignite volatile material in the environment. For purposes of brevity throughout the rest of this discussion, power is understood to mean energy and/or power.
The host-side protection circuitry may include power supply protection circuitry and/or signaling protection circuitry. The power barrier circuitry prevents power from flowing from the signal conditioner over the first wire and the second wire supplying power to the signal conditioner. The signaling protection circuitry prevents power in excess of the intrinsically safe threshold from being applied by the pick-off signal conditioning circuitry in the signal conditioner to the leads connecting the pick-off signal condition circuitry to the host system.
The flowmeter assembly barrier circuitry prevents power in excess of a intrinsically safe threshold from being applied to leads connected to the flowmeter assembly. The flowmeter assembly protection circuitry may include a drive signal protection circuitry and sensor signals protection circuitry. The drive protection circuitry prevents power in excess of the intrinsically threshold power from being applied to leads connected to the driver by the drive circuitry in the signal conditioner. The sensor signal protection circuitry prevents power from being applied to a lead connected the first pick-off and a lead connected to the second pick-off by the pick-off signal conditioning circuitry in the signal conditioner.
The host system includes the power supply and a secondary signal processing system. The power supply supplies power to the entire system and the secondary processing system receives output signals from the signal conditioner and determines properties of the material flowing through the flow tube. In order to be intrinsically safe, the host system may include a barrier that prevents power greater than the intrinsically safe threshold from being applied to leads connected to the signal conditioner by the host system.
The barrier may include power supply protection circuitry and secondary processing protection circuitry. The power supply protection circuitry prevents power in excess of the intrinsically safe threshold from being applied to the first wire and the second wire supplying power to the signal conditioner. The secondary signal protection circuitry prevents power from being applied by the secondary processing system to the leads connecting the secondary processing system to the pick-off signal condition circuitry in the signal conditioner.
An aspect of this invention is meter electronics for a Coriolis flowmeter capable of being intrinsically safe. The meter electronics may include the following components. A signal conditioner remote from a host system that receives power from a power supply in the host system via a first wire and a second wire. Drive circuitry in the signal conditioner generates a drive signal from the power received from the power supply and applies the drive signal to a driver affixed to at least one conduit. Pick-off signal conditioning circuitry in the signal conditioner receives input signals from a first pick-off sensor and a second pick-off sensor affixed to said at least one conduit, generates information indicating properties of a material flowing through the conduit from the input signals, and transmits output signals containing the information to the host system. Host-side protection circuitry in the signal conditioner prevents power in excess of an intrinsically safe threshold from being applied by circuitry in the signal conditioner to leads connecting the signal conditioner to the host system and flowmeter assembly protection circuitry in the signal conditioner prevents power in excess of the intrinsically safe threshold from being applied by circuitry in the signal conditioner to leads connecting the signal conditioner to the driver, the first pick-off sensor, and the second pick-off sensor.
Another aspect of this invention is meter electronics wherein the host-side protection circuitry includes power supply protection circuitry in the signal conditioner that prevents power in excess of the intrinsically safe threshold from being applied to the first wire and the second wire by circuitry in the signal conditioner.
Another aspect of this invention is meter electronics wherein said host-side protection circuitry includes signaling protection circuitry in the signal conditioner that prevents power in excess of the intrinsically safe threshold from being applied to leads connecting the pick-off signal conditioning circuitry to the host system.
Another aspect of this invention is meter electronics wherein the flowmeter assembly protection circuitry includes drive protection circuitry in the signal conditioner that prevents power in excess of the intrinsically safe threshold from being applied by the drive circuitry to leads connected to the driver.
Another aspect of this invention is meter electronics wherein the flowmeter assembly protection circuitry includes sensor protection circuitry that prevents power in excess of the intrinsically safe threshold from being applied by the pick-off signal conditioning circuitry to leads connecting the first pick-off sensor and the second pick-off sensor to the pick-off signal conditioning circuitry.
Another aspect of this invention is meter electronics wherein the signal conditioner is operating intrinsically safe.
Another aspect of this invention is meter electronics wherein the host system includes the power supply and a secondary signal processing system. The meter electronics further comprises a barrier in the host system that prevents power in excess of the intrinsically safe threshold from being applied by the host system to leads between the signal conditioner and the host processor.
Another aspect of this invention is meter electronics wherein the barrier includes power protection circuitry that prevents power in excess of the intrinsically safe threshold from being applied to the first wire and the second wire by the power supply.
Another aspect of this invention is meter electronics further comprising secondary processing protection circuitry that prevents power in excess of the intrinsically safe threshold from being applied by the secondary processing system to leads connecting the pick-off signal conditioning circuitry to the secondary processing system.
Another aspect of this invention is meter electronics wherein the output signals are applied to the first wire and the second wire by the pick-off signal conditioning circuitry.
Another aspect of this invention is meter electronics wherein the output signals are applied to a third wire and a fourth wire that are connected to the host system.
Another aspect of this invention is meter electronics wherein the drive circuitry controls the amount of current of the drive signal that is applied to the driver.
Another aspect of this invention is meter electronics wherein said drive circuitry controls the amount of voltage of said drive signal that is applied to said driver.